There are some days a person may have bad times in his life, feeling down and hopeless about reaching his goals or achieving his dreams, a person may feel those feelings for a while, sometimes months.
A person may feel he do not have what it takes for himself to achieve his goals, due to his own feelings, ideas or outside pressure. Sometimes even if a person is strong and stick to his own opinions (most of the times) outside pressure, peer pressure is able to control him, his perception. Such as if he had a goal he wants to reach but everyone around him tells him continually he could not, most of the time he will stop working on reaching his goal and when time passes (months) eventually most of the times he will loose faith in his abilities to reach the goal.
I know a person should not be easily controlled by others but sometimes a person cannot do anything. I love writing and reading. I suggest a person writes his accomplishments, when on his happy and and everything in his life to going good. He writes down his accomplishments so he reminds himself about them and can read them later when ever he needs a self trust boost